Basics

Air Flow Basics

-Air is invisible-Everyone assumes adequate airflow-Frequently airflow is 30%-50% low-Cooling – 400 CFM per ton-Heating – 100 to 500 CFM /10,000 BTU-Duct leakage or high static pressure-Air properties must be measured

Basics

•Low airflow can cause temperature stratification

•More fan power is not always the answer

•Select equipment based on available airflow – 400 CFM

•Inadequate air flow can waste 10% in energy

•400 CFM per ton wet coil needed

•Select equipment with reserve CFM

•Freeze-up occurs at 200 CFM per ton

Air Flow Basics

Basics

The Equipment Or The System?

-If the problem is with the equipment, the solution is up to you.

-If the problem is with the air distribution system, the primary responsibility for the solution lies elsewhere, and/or possibly you.

Basics

Correct Air Flow

•You cannot get the performance from an air conditioner without it

•You cannot accurately charge orifice or capillary tube systems without it.

•So, how do we determine it?

Correct Air Flow

• Total Static Pressure

• Temperature Rise

• Evaporator Pressure Drop

System Static Pressure

Measurement

System Static Pressure

(See Handout)

Static Pressure Measurement

-The key to system airflow diagnostics

-A companion to airflow measurement-It takes less than 5 minutes to measure

-Similar to blood pressure diagnostics

Total External Static Pressure+.65” (Supply side reading) -.45” (Return side reading)

1.10” Total External Static Pressure

System Static Pressure

(See Handout)

CFMBy

TemperatureRise Method

Airflow Measurement(Temperature Rise Method)

(Red Book, Pg. 33)

CFM By Temperature Rise

BTUH OUTPUT

T X 1.08*= CFM

*1.08 = constant number for std air. It’s a combination of a number of values that are in the complete equation. Std air is 70F, sea level

CFM By Temperature Rise

•425 CFM Per Ton (Wisc.-Dry Coil)

•Humidifier bypass closed

•Switch Heating and Cooling Speed Tap!!!

•Relocate Heating Speed tap to proper speed!

Blower should always be on high speed?

•2 TON – 800 CFM

CFM

By Evaporator Pressure Drop